Hey a friend of mine had this problem recently and was very upset that someone trying DCC send as well as DCC chat would disconnect him from the server. We managed in the end to completely disable DCC so that this would not happen, although he cannot use DCC now he can no longer be disconnected by another person. We never did figure out the real problem behind it.
Here's what we did if you'd like to try it:
Options - DCC: tick both "ignore all"
Options - DCC - Ignore: select "accept only" in Method box, then delete all file extensions in the box below that, then tick "turn ignore back on in 3 min"
Options - DCC - Server: there must be no ticks in any of the boxes
I hope this helps you out
Please re-check these settings after changing them as they like to change themselves back under certain conditions
[EDIT] If anyone does know/find out why this happens please could you let me know.